单项填空（共15小题；每小题1分，共15分）
从每题所给的A、B、C、D四个选项中，选出可以填入空白处的最佳选项，并在答题卡上将该项涂黑。
21. --Is your uncle a pilot?
--Yes. He _________ four days a week and has been to many places.
A. travels B. travelled C. has travelled D. had travelled
22. James was enjoying the art show, _________ his wife wanted to go home.
A. or B. for C. so D. but
23. --Was the United State of America founded on July 4th, 1776？
--You _________ be right but I need to check it in the history textbook anyway.
A. have to B. must C. may D. will
